1. Field of the Invention
The present invention relates generally to steering axle suspension for a heavy truck. More specifically, the present invention relates to an independent front air suspension for the steering axle of a heavy truck.
2. Prior Art
Independent front axles are universally applied in passenger cars and light trucks. In most cases such vehicles use coil springs (typically in a vertical position) or leaf springs. Independent front axles (or "suspensions") allow each of the front steering wheels (left and right) to absorb shocks independent of one another. Although their use is pervasive in automobiles, they have not been used in heavy trucks.
There are two primary reasons for the absence of independent front suspensions in trucks. The first is that trucks are designed to haul freight and not as pleasure vehicles. Cars, on the other hand, are designed for comfortable transportation. Independent front suspensions significantly further this end because with an independent front suspension road bumps and other disturbances of a smooth ride affecting one wheel are reacted in that wheel suspension assembly without affecting the other wheel. In a typical non-independent front suspension of prior art trucks, an impact or articulation affecting one wheel also affects the other wheel (because they are connected together through an axle beam) causing a more turbulent disturbance of the overall vehicle ride characteristics. The second reason is that trucks must have more sturdy suspension components to support the great weight they carry. These large components take up most of the available space, so much so that prior art independent front suspensions do not fit.
Prior art attempts to create an independent front suspension in a heavier vehicle include those attempts to provide the same in transit coaches (buses). A common prior art approach in this context is to install air springs for each wheel in a vertical position such that the air spring centerline is compressed in a vertical plane during suspension articulation. The prior art is characterized by this approach of suspension air spring mounting.
While transit coaches have front axle capacity similar to that of a Class 8 highway tractor (defined as having 33,001 lb. gross vehicle weight and up), their chassis arrangement is very different. Transit coaches typically have rear engine installations, narrow center beam frames and horizontal mounting of the steering gear. In such an arrangement there is room to mount the air spring vertically. This is not the case, however, in heavy trucks.